1. Field of the Invention
This invention relates to capacitance gauge apparatus for the direct measurement of surface texture.
2. Description of the Prior Art
The utilization of electrical capacitance techniques for monitoring surface texture is broadly old and appears to have been first suggested by J. Perthen "Ein neuses Verfahren zum Messen der Oberflachengute durch die Kapazitat eines Kondensators," J. Maschinenbau Betrieb. 1936 (December), 669. A general theoretical treatment of the subject of capacitance gauging appears in the Proc. Instn. Mech. Engrs. 1967-68, Paper 31, entitled "Surface Finish Assessment by an Electrical Capacitance Technique" by K. F. Sherwood and J. R. Crookall.
The British Ministry of Defense has developed an electrical capacitance device, covered by British Pat. No. 818,345, which uses a spring mounted rigid, small area probe as one element of the capacitor. This arrangement does not appear to produce good discrimination.
The apparatus of the instant invention proposes to use a different type capacitance circuit and probe wherein a plate member is resiliently supported so as to better conform to the undulations of the surface being monitored. Additionally, a novel cooperating circuit distinguishes between capacitance magnitudes in the order of a fraction of a picofarad and provides for accurate accumulation of the discharge pulses which are generated as the capacitance probe measures the conductive surface, the texture of which is to be evaluated.